We're not running any giveaways for NBA 2K15, and I don't think you'll find anyone who's doing so two years after its release. If you're interested in picking it up, your best bet would be to wait until it goes on sale on Steam, Green Man Gaming, etc, which older 2K titles do from time to time.

Of course, if someone does have an unused Steam key they're willing to gift to you, then that's their call to make. I can't help you out there though, sorry.